In the past, a coating type of magnetic recording media has been generally employed. This type of media is generally obtained by coating on a nonmagnetic support a magnetic coating composition prepared by dispersing a powdery magnetic material, e.g., a magnetic powder of an oxide such as .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, a Berthollide compound composed of .gamma.-Fe.sub.2 O.sub.3 and .gamma.-Fe.sub.3 O.sub.4, CrO.sub.2, etc., a ferromagnetic alloy powder, or so on, into an organic binder. Some conventional binders include vnyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, epoxy resin, and polyurethane resin. The coated composition is then dried to form a magnetic layer.
In recent years, there has been a demand for recording a large amount of information in a small area of recording material, which is commonly referred to as "high density recording".
With the increased demand for high density recording, there has been an increased demand for the so-called non-binder type of magnetic recording media. Such media contain no organic binders in their magnetic recording layer(s) and have as the magnetic recording layer(s) a thin film(s) of ferromagnetic metal(s) formed by the vapor deposition techniques such as vacuum evaporation, sputtering, or ion plating, or metal plating techniques such as electroplating or electroless plating. Such media have attracted the attention of the art, and various efforts for putting them to practical use have been made.
Conventional coating type magnetic recording media principally utilize metal oxides as magnetic materials. Furthermore, reduction of the thickness of such media is accompanied by a lowering of the signal output. Therefore, reduction of the thickness of the magnetic recording layer, which is necessary for increasing the recording density, is limited. In addition, they must be manufactured by complicated processes using large sized incidental equipment for recovering solvents used in the manufacturing process. Such equipment and procedures may also involve problems of environmental pollution. On the other hand, non-binder type magnetic recording media contain ferromagnetic metals, which have saturation magnetization greater than those of the above described metal oxides. Such media are in the form of a thin film which does not contain any nonmagnetic substances such as a binder. Therefore, such media can have very thin magnetic films capable of high density recording. In addition, the manufacturing processes are simple.
Magnetic recording media used for high density recording must use magnetic substances having high coercive force and a reduced thickness. Such being the case, non-binder type magnetic recording media appear to be very promising because their thickness is 1/10 less than thickness of the conventional coating type magnetic recording media. Furthermore, such media possess high magnetic flux densities.
In particular, the application of vacuum evaporation techniques to the formation of magnetic recording layers is advantageous because it is not necessary to dispose of waste solutions, unlike metal plating techniques, because of the simple manufacturing process, and because the deposition speed of the magnetic metal film can be increased to a high rate. There are known processes for manufacturing a magnetic film having coercive force and squareness ratio desired for magnetic recording media by utilizing vacuum deposition processes, e.g., an oblique incident evaporation method, as disclosed in U.S. Pat. Nos. 3,342,632 and 3,342,633.
Further, magnetic recording media provided with ferromagnetic metal thin films must have high corrosive strength. It is also desired that there is little or no decrease or unintentional erasure of signals recorded in the magnetic recording medium with the lapse of time, for example, that caused by corrosion or rust during storage.
Various methods for improving the weather resistance of magnetic recording medium have been proposed. For example, in Japanese Patent Application (OPI) Nos. 198543/82 and 17544/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") a method in which a magnetic vapor deposition film is formed on a non-magnetic support moving along a rotating drum and the film is exposed to an oxidizing atmosphere while it is moving along the drum is described. However, even if this method is employed, the weather resistance is not necessarily improved and the adhesive property between the film and the support is not sufficient.